Transmitter and/or receiver circuits



ardi l, 1949. E. L. GINZTQN 2462 856 TRANSMITTER AND/OR RECEIVER CIRCUITS Fired May 19, 1942 2 Sheets-Sheet 1 LOW I POWER 7 7 so RCF aao TUNABLE POWER 7 AMPLiFIER FIG, 2

+ MODERATE TIME CONSTANT CIRCUIT 233 SUM RELAY 205 cmcuu ZERO TIME CONSTANT CIRCUIT INVENTOR E.L.GINZTON fi z/5 25 2; L

March 1, 1949. E. a... GHNZTON 2 452856 TRANSMITTER AND/OR RECEIVER CIRCUITS Filed May 19, 1942 I 2 Sheeis-Sheet 2 AUDIO AMI? 252 25 3 ET Tl l lNVENTOR EDWARD LGENZTON Patented Mar. 1, 1949 TRANSIHITTER AND/ OR RECEIVER CIRCUITS Edward L. Ginzton, Wantaugh, N. Y., assignor to The Sperry Corporation, a corporation of Delaware Application May 19, 1942, Serial No. 443,604

24 Claims. 1

This invention relates, generally, to transmitter and/or receiver circuits wherein means are provided for maintaining oscillators or amplifiers either at a fixed operating frequency or at an operating frequency determined by a master unit or by an incoming signal.

In the operation of transmitters and receivers, and specifically ultra high frequency transmitters and receivers, it is highl desirable that the transmitters be operated at as nearly fixed frequency as possible and that maximum output be maintained regardless of disturbing influences, such as changes in operating parameters, and that receivers be compelled to follow as closely as possible Variations in the frequency of the incoming signal while operating at a maximum output. While the invention is disclosed in connection with ultra high frequency transmitter and receiver circuits it is understood that the same is not limited thereto but can be applied to other apparatus with equal facility, i. e., wherever tracking is desired or where maximum output is desired.

One object of the present invention is to provide means for causing the power amplifier of a transmitter to exactly track the oscillator used in conjunction therewith.

Another object of the present invention is to provide a maximizing device adapted for maintaining equipment at maximum output such, for example, as maintaining an oscillator at maximum output by use of memory circuits so designed that the system will search out the proper position of the control means to obtain a maximum output.

Other objects and advantages will become apparent from the specification, taken in connection with the accompanying drawings wherein the invention is embodied in concrete form.

In the drawings,

Fig. 1 is a schematic wiring diagram of a preferred embodiment of the invention applied to a transmitter power amplifier provided with memory circuits operating to maintain it at maximum output.

Fig. 2 is a schematic wiring diagram of another embodiment of the invention similar to Fig. 1.

Fig. 3 is a schematic wiring diagram of a further embodiment of the invention wherein the 2 principles shown in Figs. 1 and 2 are applied to a receiver.

Similar characters of reference are used in all of the above figures to indicate corresponding parts.

Referring now to Fig. 1, the reference numeral I designates an oscillator illustrated as a low power source, preferably of the type disclosed in Patent No. 2,242,275, issued May 20, 1941, in the name of R. H. Varian, for Electrical translating system and method. The oscillator I may be used. by itself or may be used as the upper end of a stabilized frequency multiplication chain such as a crystal controlled chain. Energy is supplied from the output or catcher resonator of source I through a concentric line 3 to the buncher resonator 5 of an amplifier 4 of the type disclosed in the above mentioned patent. inergy from the power amplifier i is s pplied from catcher resonator 6 thereof through concentric line 1 and radiated as from a dipoie antenna 1' attached thereto.

A maximum finding device useful for keeping apparatus at its output is also shown in Fig. 1. In this figure the device is shown applied for keeping the catcher resonator B of the power amplifier l tuned to maximum out put through concentric line a to the antenna 7'. The buncher resonator 5 is shown excit with ultra high frequency energy sup a concentric line 3 connected ther said line being fed from low power 0s A concentric transmission line 2% coupied to catcher resonator 5 supplies a small amount of energy to a detector 262 of any suitable type, such as a crystal rectifier, the detected output of which appears as a voltage across its lead resistor 311i and is fed into two time constant circuits 204 and 265, which circuits are respectively moderate or shortand zero-timaconstant circuits. These circuits comprise tricde tubes 2!)? and 208, respectively, whose grids are connected to the grounded (negative) terminal of resistor 3M and are thereby controlled from the output of detector 202. The tube 297 of the short-timeconstant circuit 204 has a plate circuit including plate battery 2'" and a resistance 2H which is bridged by a condenser 2M which is of mod erate size so as to give this circuit a short-time constant of preferably around one second or less.

Tube 2838 of substantially zero-time-constant circuit 2% has a plate battery 2% in series with resistance M2 its plate circuit, which resistance 2 I2 is bridged by a very small condenser 2 l5 which gives this tube a very short or substantially zero time-constant, so that the current in this tube instantly responds to changes in its voltage. The cathode-biasing resistors of tubes 2E! and 238 and their batteries 2?? and H8 are selected to cause tubes 2t? and 288 normally to pass current, and to make the potentials of their plates normally equal.

Two sum or combining circuits 22E and 222 are employed. The circuit 22l consists of the two tubes 22'! and 22? whose plates are respectively connected through respective opposed field windings 3i and iii of tuning motor 32 to a common plate battery 3S2 and thereby to their cathodes. The rotor of this motor 32 is connected to drive the shaft 236 carrying pinion 23? which operates rack 24% of a tuning plunger which varies the resonant frequency of resonator 5. Motor 32 is of the type which is stationary when equal currents flow through its field windings 3!, l, and which rotates in one direction or the other according as the current in winding 3 exceeds or is less than that in winding ii. The direction of rotation of motor 32 may also be reversed by reversing the polarity of the voltage applied to its armature.

The joined cathodes of tubes 22'! and 22? are connected to ground through a common cathodebiasing resistor 225. The grids of these tubes are connected to ground through respective input resistors 223 and 223. The grid of tube '22? is connected to the positive terminal of battery SE6, whose other terminal is grounded. The grid of tube 22? is connected to the negative terminal or a battery 2H3 whose positive terminal is connected to the plate of zero-time-constant tube Hie voltage of battery 2E8 is selected to oppose and to be substantially equal to the voltage between the plate of tube 288 and ground, when no voltage appears across detector load resistor see; that is, when no oscillations exist in resonator 5, due to its resonant frequency being widely different from the frequency of the input from source 5. Hence, under this condition, no voltage appears across resistor 223.

In the absence of potentials applied to the grids of these tubes 22?, 22?, equal currents are supplied to the two windings 3!, 3! of motor 32, so this motor is stationary. If desired, tubes 22?, 22'5" may be adjusted just to cut-off so that no current will be supplied to either winding Si or St for zero grid voltages. Battery 2H6 serves to impress a voltage across resistor 223 making the potential on the grid of tube 227 more positive and causing tube 22? to pass more current and thereby drive motor 32 to actuate the tuning plunger 25.6 in a certain direction. This plunger are continues its motion until the end of travel thereof whereupon a trip lever 239 actuates a reversing switch 2M which reverses motor 32 so that this motor drives the plunger in the reverse direction. In this way, the resonant frequency of resonator 6 is periodically varied or scanned across a frequency range until it coincides with the frequency of the energy supplied to input line 3.

Assum ng that during the travel of the plunger the amplifier becomes tuned to the incoming signal from source 6, a negative poten- .l from detector 232 is applied to the rid of tube 2%, thereby decreasing the current passed by tube 298, and making its plate more positive. This action is substantially instantaneous, since the time constant of resistor 2i2 and condenser 2E5 is almost zero. This action at once makes the grid of tube 22'? more positive, and so that tube 22'! passes more current to winding 3i, which bucks win-ding 3! and hence reduces the speed of motor 32.

Preferably, the voltage of battery 3 i 8 is selected to be substantially equal to the maximum voltage produced across resistor 223' when resonator 6 is excited to maximum amplitude of oscillation; that is, when resonator ii is tuned to resonance with the input supplied by line 3. This Way, motor 32 will stop upon reaching proper tuning of resonator 5, since then the voltage across resistor 223 will be equal to the Voltage of battery 3H3, producing equal excitation of windings 3i, 3!, which then neutralize one another to stop motor 32. If this condition of equality cannot be obtained, the battery voltage is selected to be as large as the maximum voltage across resistor 223 which is expected. to occur during operation. Then motor 32 will run at least until the proper tuned condition is reached, although it may tend to run past this position. It is desirable that the battery voltage be not smaller than'the resistor 223 voltage, since otherwise the motor will stop before true resonance is attained.

The second combining circuit 222 has two tubes 228, 228' with a common grounded cathode biasing resistor 22%. The grids of these tubes are connected to ground through respective input resistors 22 i, 22 i, and are also connected respectively to the plates of tubes 29'! and 268 through respective batteries 2i! and H8, which oppose plate batteries 2?? and 273. The voltages of batteries Eli and 248 preferably are substantially equal respectively to the voltages of batteries 2T3, 218 less the respective volt drops in resistors 2| i, 2!? due to normal current therein (for zero grid voltage of tubes 201, 263), so that normally zero voltage is impressed across input resistors 225, 224.

A relay 233 has two opposed coils 22%, 225i connected respectively in the plate circuits of tubes 228, 228'. The armature 231 of relay 233 is normally in the position shown, and connects battery 232 to the armature of motor 32, by way of leads 230 and through reversing switch 2 4i, If the output current of tube 228 is greater than that of tube 228', the action of coil 229 overcomes that of coil 229', and the relay armature 235 is kept pulled toward coil 229, as shown, to place the battery 232 across the leads 239 in one sense. If the current through coil 229' is greater than that in coil 229, the battery 232 is placed across leads 230 in the opposite sense, and motor 32 Will run in the opposite direction. Thus, the direction in which motor 32 operates is determined by whether the potential of the grid of tube 228 is greater than that of tube 223 or vice versa.

In operation, assuming that amplifier t is operating far from its resonant frequency, the action of battery 3E6, circuit 22! and reversing switch 24! scans the operating frequency range until resonator 5 is tuned to a frequency near that of source i. Then a voltage appears across resistor 3M, and the current in both tubes 298 and 23: decreases. The current in tube 2% decreases faster than that in tube 261, due to the difference in the time constants of the plate circuits of those tubes. Thus, the potentials of the grids of tubes 228 and 228 both become more positive, but that of tube 228 changes positively more quickly. The current in relay coil 229 therefore remains greater than that in coil 229, and relay armature 23! remains in the position shown. Motor 32 therefore continues to tune resonator 6 toward resonance with the input wave.

So long as exact resonance is approached, the voltage across resistor Sill continues to increase, and the current in coil 2'29 continues to exceed that in coil 229. However, when the resonant condition is passed, the amplitude of oscillation of resonator 6 (and hence the voltage across resistor 38!) decreases, instantaneously increasing the current in tube 208. The potential of the grid of tube 228 thus becomes more negative, decreasing the current in coil 229. The current in coil 22$, however, does not change at once, due to the time constant of resistor 2H and condenser 2M. Therefore, coil 229 attracts armature 23! and reverses motor 32, which then again returns resonator 6 to be resonant with the incoming wave from source l. The resonant frequency of resonator 6 thus is caused to hover about the frequency of the input signal.

For the above operation to be maintained, it is necessary, of course, that the voltage of battery 356 be equal to or greater than the largest voltage produced across resistor 223' by virtue of the variation in voltage across resistor 39!. It is desirable that battery 3% be equal to the voltage across resistor 223' when resonator 5 has its maximum amplitude of oscillation, since then, when the resonator is exactly tuned to the incoming signal supplied through line 3, the out put of the zero time constant circuit 295 as supplied across resistor 223' exactly opposes the voltage of battery 355 as applied to resistor 223, so that the net field of motor 32 is zero, and hence this motor does not operate in either direction and resonator is kept at resonance.

Now if it be assumed that, for some reason, amplifier l starts to operate at one side of its input frequency, then the output of tube 208 will at once fall oil. Since the output of battery Bib is fixed, a differential field will be produced for motor 32 and this motor will start to operate to move plunger 248 in one direction. However, so far the direction of rotation of motor 32 has not been determined, and it merely operates in one direction or the other. If the rotation is in the correct direction, so that the resulting tuning brings the peak of the resonance curve of the amplifier back to the input frequency, then the diiference between the outputs of channels 2G5 and 2535* will be of positive polarity, indicating that the magnitude of oscillation in the amplLfier t is building up, and the motor will continue to rotate in the same direction, since relay 23! will remain in its position shown in Fig. 1. The rotation continues until the output of amplifier t is a maximum, at which time the rotation will automatically stop since the volt-drops across 223 and 223' will then be equal. If the motor 32 actually started turning in the Wrong direction, then the difference between the outputs of channels 255 and 204 will be negative, and this would reverse the direction of rotation of motor 3'2 due to the tripping of relay It will thus be seen that this device of Fig, l in a sense simulates manual tuning. In tuning any device to the maximum setting, one first observes what the output of the device should be, as provided here by battery 3IB. Then one arbitrarily moves the tuning knob and finds out whether or not the result is an improvement in the output, corresponding to the action of channels 2M and 2&5, which indicate whether the motor is turning in the proper sense.

An approximation to having the voltage of battery 3E8 equal to the voltage produced across resistor 22-3 at maximum oscillation of resonator 6, can be obtained by use of a long (substantially infinite) time constant circuit 293, shown in Fig. 2, in place of battery 31%.

Circuit 233 is similar to circuits 264, 285, having a tube 256 with a long time constant circuit in its plate circuit, formed by resistors 209 and condensers 2i3. The grid of tube 2516 is also connected to resistor 335. Suppose amplifier 4 is properly tuned. Circuit 293 then effectively remembers what the condition of amplifier 4 is, so that, should any deviation from the desired condition occur, circuits 2% and 265 will restore amplifier 4 to its previous condition as determined by circuit 263.

Thus, instead of an infinite time constant determining the operation of motor 32, i. e., that provided by battery 3H5, a somewhat shorter time constant is now substituted, namely that provided by circuit 253. It will be noted that channel 283 in operation effectively remembers what the output of detector 292 was when resonator 6 was perfectly tuned, channel 265 tells the motor 32 whether or not the detector output is more or less than it was a short time ago, and channel 285 determines whether or not the motor is turning in the right direction. That is, circuit 295 Will cause motor 32 to retune am plifier 4 until balanced by circuit 263, the direction of rotation of motor 32 being determined by circuits 2M and 265 as before.

Fig. l is desirable when the apparatus is just starting up, for at that time the resonator 6 is completely detuned, the batter 3l6 then serving as a reference to determine what is eX- pected of the amplifier 3. However, after accurate tuning is once effected, Fig. 2 is desirable, so that the long time constant circuit 203 will determine the voltage across resistor 223 and control the operation. It will be obvious that a simple switch, such as switch 3i? of Fig. 2, may be used to transfer from the Fig. 1 system to the Fig. 2 system, after accurate tuning is accomplished by the Fig. 1 device.

If desired, two separate systems of the type of Fig. l or 2 may be used to separately tune resonators 5 and 6 or one such system may be caused to alternately tune these resonators by use of a commutator. The latter arrangement is illustrated in Fig. 3. In this figure the output of an entire receiver system is used to achieve proper tuning of the resonator rather than using the output of a crystal to maximize the output of the resonators, as in Figs. 1 and 2. In Fig. 3, the system of Fig. 2 is employed to maximize the output of a detector in the utilization channel of an ultra-high-frequency receiver of the superheterodyne type. The buncher resonator 243 of amplifier-detector 2 52 of Fig. 3 is shown receiving signal energ through line 245. Energy from a local oscillator is fed into the catcher resonator 254 by Way of line 246'. The output from detecting-plate 24-8 is then an intermediate frequency wave modulated by the intelligence frequencies. This intermediate frequenc wave is applied directly to the intermediate frequency amplifier 269, thence to detector 25! and audio amplifier 255, and thereby to the utilization device such as car phones 254. The detected direct-current component of the output of detector 25! is applied as before to three channels, namely an infinite-large-time-constant circuit 283, a shor -time-constant circuit 2M and a zero-time-constant circuit 265'. The outputs of these channels are applied as in Fig. 2 to sum circuits 22!, 2222. The output of sum circuit 225, as before, may be applied directly to the field coils of a direct-current motor for retuning both resonators 243, 2 54 if desired, or for tuning the single resonator 244 as illustrated. The output of sum circuit 222 may be applied through reversing rela 233 to the armature of the same motor. In Fig. 3 the outputs of the two sum circuits 22 i 222 are shown commutated by half-conductor, hali-insulator commutators 263, 263' cooperating with relays 257, 257 and switches 258, 258. The commutators 263, 263 are shown continuously driven by a motor 26 Thus, in operation the outputs of sum circuits 22i', 222 are used alternately for controlling tuning motors iii 2%, each tuning operation being or" a sufficient length of time to efiect the required tunin Obviously, by using additional commutators more than two tuning controls may be operated.

Although Figs. 1 to 3 have been shown as illustrated in connection With maximizing the output of a high frequency tube, these circuits are equally applicable for maximizing the output of any device where a voltage signal can be produced responsive to the output of the device and having a control member adapted to be driven by a motor and for adjusting the output of the device.

As many changes could be made in the above construction and many apparently Widely diiierent embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or hown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In apparatus of the character described, means for producing energy, and means for controlling said energy-producing means to maintain the latter at maximum output, said controlling including means for supplying a potential responsive to the magnitude of the output of said energy producing means, a plurality of time-constant circuits connected for receiving said potential, the time constants of said circuits being different from one another, sum circuits supplied from said time-constant circuits, motive means connected for controlling the output of said energy producing means, said motive means being connected to be controlled from said sum circuits.

2. Apparatus as defined in claim 1 wherein said motive means comprises a plurality of separate motive devices, and wherein commutating devices are in luded n the connection between said motive d vices and said sum circuits for effecting alternat operation of said motive devices.

3. In apparatus of the character described, a tunable device, a long-time-constant circuit, a short-time-constant circuit and a zero-time-constant circuit coupled to said device, a pair of sum circuits, the first of said sum circuits being connected to said long-time-constant and to said zero-timeccnstant circuit, and the second of said sum circuits being connected to said zerotime-constant circuit and to said short-time-constant circuit, motive means for tuning said device, said first sum circuit being connected for starting and stopping said motive means, and said second sum circuit being connected for determining the direction of operation of said motive means.

4. In apparatus for maintaining maximum output amplitude from a device producing a potential responsive to said output amplitude, means controlling said device to vary the output amplitude thereof, and a plurality of control circuits responsive to said amplitude having different time constants and connected jointly to control jointly said controlling means, said circuits being responsive to said potential.

5. In the apparatus defined in claim 4:, said controlling means comprising a motor, means connecting certain of said control circuits to said motor for effecting reversible actuation of said motor, and means connecting certain of said control circuits to said motor for selecting the proper direction of actuation of said motor.

6. In apparatus for automatically controlling the frequency of a variable frequency device, the combination comprising means for tuning said device including motor means, a plurality of control circuits having different time constants connected to the output of said device, means connecting certain of said control circuits to said motor means for effecting reversible actuation of said motor means, and means connecting certain of said control circuits to said motor means for seiecting the proper actuation of said motor means.

7. In apparatus for automatically controlling the frequency of a variable frequency device, a detector connected to the output of said device, tuning means for said device, reversible motor means coupled to said tuning means, control circuits connected to the output of said detector for actuating the motor means, one of said control circuits serving to effectively remember the output of said detector when the device is properly tuned, another of said control circuits serving to effectively detect deviations of said detector output, and another of said control circuits for determining the direction of actuation of said motor means, and means connecting said control circuits to said motor means.

8. Apparatus for automatically controlling the frequency of a variable frequency device, a plurality of individual tuning means and motors for each tuning means, a plurality of control circuits having different time constants, integrating circuits connected to said control circuits, and commutator means alternately connecting said integrating circuits for controlling the respective motors.

9. In apparatus for controlling a variable frequency high frequency device, reversible motordriven means for tuning said device, a plurality of control circuits having different time conconnected with the output of said device, three of said control circuits being substantially of zero, relatively smail and large time-constants respectively, means including an inte rating circuit connecting large and Zero-time-constant control circuits to said reversible motor-driven means, a relay circuit including a reversing switch connected to said motor-driven means, and a second integrating circuit connecting said smalland zerc-timewonstant circuits to said relay circult to determine the proper direction of rotation of the motor-driven means.

10. The apparatus defined in claim 9, wherein said motor-driven means includes a plurality of tuning means for said device and a reversible motor for each tuning means, switching means for alternately connecting-said first integrating circuit to said motors, a second switching means for alternately connecting said relay circuit to said motors, and commutator means controlling actuation of said switching means.

11. Apparatus for tuning a resonant circuit to resonance with an applied frequency, comprising means for tuning said circuit, means responsive to change in the amplitude of oscillation of said circuit for actuating said tuning means, and means responsive to the sense of said change in oscillation amplitude for controlling the direction of actuation of said tuning means.

12. Apparatus as in claim 11, wherein said actuating means comprises a long-time-constant circuit and a zero-time-constant circuit both responsive to said oscillation amplitude, and means diiieren tially responsive to said time-constant circuits for actuating said tuning means.

13. Apparatus as in claim 11, wherein said sense-responsive means comprises a short-timeconstant circuit and a sulostantially zero-timeconstant circuit both energized by said oscillation amplitude, and means differentially responsive to said time-constant circuits for controlling the direction of actuation of said tuning means.

14. Apparatus for maximizing the output amplitude of a variable output device, comprising means responsive to a change in output amplitude of said device for adjusting said output amplitude in an arbitrary direction, and separate means responsive to the sense of said arbitrary adjustment for controlling said adjusting means to increase said output amplitude.

15. Apparatus as in claim 14, wherein said sense-responsive means comprises means for comparing the instantaneous output of said device with its output at a prior time and means for controlling said adjusting means in response to the polarity of the difference between said output values.

16. High frequency apparatus, comprising a mixer-detector having a pair of tuned circuits, means for supplying an input wave to be demodulated to one of said circuits, means for supplying a local oscillator wave to the other of said circuits, means for deriving an intermediate frequency wave from said mixer-detector, means for detecting said intermediate frequency wave, and means responsive to the output of said detecting means for controlling the tuning of said circuits into resonance with said input wave and said local oscillator iwave, said last-named means comprising independent tuning means for said circuits and commutator means for actuating said tuning means alternately and successively in response to said detecting means output.

17. Apparatus as in claim 16, wherein said tuning controlling means comprises means responsive to a change in amplitude of said detecting means output for initiating operation of said tuning means, and means responsive to the sense of said amplitude change for controlling the direction of operation of said tuning means.

18. High frequency apparatus, comprising mixer means having a tuned circuit, means for supplying a received wave and a local oscillator wave to said mixer means, means for deriving an intermediate frequency wave from said mixer means, and means responsive to said intermediate frequency wave for controlling the tuning of said mixer, said tuning control means comprising means for tuning said mixer, means responsive to a change in the amplitude of intermediate frequency wave for initiating operation of said tuning means, an means separately responsive to the sense of said amplitude change for controlling the direction of operation of said tuning means.

19. High frequency power amplifier apparatus for amplifying a wave of predetermined frequency, comprising amplifying means having a tuned circuit, means for tuning said circuit, means responsive to a change in the amplitude of oscillation of said circuit for actuating said tuning means, and means responsive to the sense of said oscillation amplitude change for control ling the direction of actuation of said tuning means to retune said circuit into resonance with the frequency of said wave.

20. Hi h frequency superheterodyne receiver apparatus, comprising an electron discharge device having a pair of cavity resonators tuned respectively to the received wave and the local oscillator frequency, and having means for prcjecting an electron beam successively through said resonators and for detecting variations in the velocity of said electrons, means for supplying a received wave to the resonator tuned thereto, means for supplying a local oscillator wave to the other of said resonators, means connected to said detecting means for deriving an intermediate fr quency wave, and means for automatically maintaining said resonators tuned to said waves, said last means including means responsive to change in amplitude of said intermediate ire-- quency wave for tuning said resonators, and means responsive to the sense of said amplitude variation for controlling the direction of operation of said tuning means.

21. Ultra high frequency apparatus, comprising a source of received signal, a source of ocal oscillator frequency, a mixing device comprising a pair of spaced hollow resonators and means for passinan electron beam successively through said resonators, means for coupling each one of said sources to a. difierent resonator, and detector means in the path of said beam beyond said resonators for producing an intermediate frequency from said device.

22. In apparatus for automatically maintaining maximum power output from a variable frequency device having its power output dependent upon its frequency, the combination comprising means for tuning said device, means for obtaining a. signal corresponding to the amplitude of said power output, a plurality of control circuits having different time constants connected to said last-named means and all responsive to said signal, and means connecting all said control circuits to said tuning means to actuate said tuning means to maintain said device at optimum frequency for obtaining maximum power output therefrom.

23. Automatic control apparatus comprising a vaiable output device, means for adjusting the output of said device, means for deriving a signal corresponding to said output, means controlled jointly by said first signal and by a fixed signal for starting and stopping said adjusting means, and means controlled jointly by said first signal and a delayed version of said first signal for determining the direction of operation of said adjusting means.

24. Automatic control apparatus comprising a variable output device, means for adjusting the output of said device, means for deriving a first REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,626,724 Demarest et a1 May 3, 1927 1,919,976 Fitz Gerald July 25, 1933 2,044,749 Usselrnan June 16, 1936 2,058,411 Carlson Oct. 27, 1936 2,106,776 Trevor et a1 Feb. 1, 1938 Number 12 Name Date Smith et al Apr. 12, 1938 Van Loon Mar. 28, 1939 Holden Apr. 18, 1939 Gerth et a1 Sept. 26, 1939 Case Oct. 3, 1939 Robinson Mar. 19, 1940 Trevor Nov. 12, 1940 Hahn Nov. 26, 1940 Schulze-Herringen Jan. 28, 1941 Varian June 17, 1941 Andrews Nov. 11, 1941 Samuel May 5, 1942 Bellescize May 26, 1942 White June 30, 1942 Varian et a1 Sept. 8, 1942 Roberts Dec. 8, 1942 Harrison Apr. 13, 1943 Hansell Jan. 25, 1944 Samuel July 2, 1946 Clark Oct. 1, 1946 Anderson Oct. 22, 1946 Samuel Nov. 12, 1946 Certificate of Correction Patent No. 2,462,856. March 1, 1949. EDWARD L. GINZTON It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 2, line 43, for the Word grounded read ungrounded; column 6, line 15, for "condensers read condenser; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 11th day of October, A. D. 1949.

THOMAS F. MURPHY,

Assistant Uommissz'oner of Patents.

Certificate of Correction Patent No. 2,462,856. March 1, 1949. EDWARD L. GINZTON It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 2, line 43, for the word grounded read ungrounded; column 6, line 15, for condensers read condenser;

and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Oflice.

Signed and sealed this 11th day of October, A. D. 1949.

THOMAS F. MURPHY,

Assistant Commissioner of Patents. 

